1. Field of the Invention
This invention relates generally to an apparatus for magnetically recording and/or reproducing video and audio signals, such as may constitute a television signal, and more particularly is directed to improvements in the recording and/or reproducing of the audio signal in such an apparatus.
2. Description of the Prior Art
In the video tape recorders according to the prior art for recording a color television signal on a magnetic tape, the chrominance and luminance signal components which constitute the color video signal are separated, and the chrominance signal component has its carrier frequency converted to a relatively low value, while the luminance component frequency modulates a relatively high frequency carrier, whereupon the frequency-converted chrominance signal component and the high side band of the frequency-modulated luminance signal component (hereinafter simply referred to as the "FM modulated luminance signal component") are mixed or combined to form a composite color video signal which is recorded on a magnetic tape in successive, parallel record tracks extending obliquely in respect to the longitudinal or running direction of the magnetic tape. In such existing system for recording a color television signal, the audio signal thereof is recorded on the magnetic tape in record tracks which extend in the longitudinal direction, that is, the running direction of the magnetic tape, and are hereinafter referred to simply as "audio tracks".
In the above-described recording system of the prior art, the oblique or slant tracks which are skewed relative to the tape and in which the composite color video signal, that is, the frequency-converted chrominance signal component and the frequency-modulated luminance signal component, are recorded by first and second substantially diametrically opposed rotary magnetic heads both supplied with the composite color video signal and alternately scanning the magnetic tape along a path at an angle to the longitudinal direction in which the tape is transported. In order to increase the recording density of the color video signal on the tape and thereby increase the duration of the recording, it has been known to restrict the speed at which the magnetic tape is transported so that the successive slant tracks scanned by the rotary magnetic heads will be closely or immediately adjacent to each other, that is, so that the space or so-called guard band between the adjacent slant tracks will be eliminated. However, in such case, the problem of "cross talk" arises in the reproducing or playback mode of the apparatus. In other words, during reproducing or playback, a transducer or head scanning one of the slant tracks for reproducing the composite color video signal recorded therein will also pick up or reproduce signals or cross talk from the next adjacent tracks.
The problem of cross talk has been substantially solved, at least in respect to the relatively high frequency frequency-modulated luminance signal component of the recorded composite color video signal, by providing the first and second rotary magnetic heads with different azimuth angles so that the composite color video signal will be recorded in each slant track by means of a magnetic head having an azimuth angle different from the azimuth angle of the head with which the composite color video signal is recorded in the next adjacent tracks. Thereafter, during reproducing or playback, each slant track is scanned by the rotary magnetic head having the corresponding azimuth angle with the result that a substantial azimuth loss is experienced as to the relatively high frequency components for the cross talk from the adjacent tracks. Thus, the cross talk in respect to the frequency-modulated luminance signal component is substantially suppressed.
However, the azimuth loss effect is rather poor in respect to the low frequency band of the cross talk, that is, in respect to the frequency-converted chrominance signal component, so that other measures need to be taken for eliminating or minimizing the low-frequency component of the cross talk. For example, as disclosed in detail in U.S. Pat. No. 4,007,482, issued Feb. 8, 1977, and having a common assignee herewith, cross talk in respect to the frequency-converted chrominance signal component situated in a relatively low frequency band is substantially eliminated by recording the chrominance signal component with different first and second carriers in the adjacent tracks, respectively. Such first and second carriers modulated by the chrominance signal component recorded in adjacent tracks, respectively, may be distinguished from each other by their respective frequency and/or polarity characteristics so that, upon reproduction of the signal recorded in a particular track, the low frequency band of the cross talk from the track, the low frequency band of the cross talk from the tracks next adjacent thereto can be conveniently suppressed or eliminated by reason of the different frequency and/or polarity or phase characteristics of the respective carriers.
More specifically, as disclosed in the above-identified patent, the chrominance signal component of the color video signal to be recorded may be frequency-converted so as selectively to produce first and second frequency-converted signals which, when considered instantaneously, have the same carrier frequency, but which differ from each other in their phase or polarity characteristics. In this case, each of the line areas or increments of one track may have recorded therein a frequency-converted chrominance signal component with a carrier of constant polarity, while, in the next adjacent tracks, the carrier of the frequency-converted chrominance signal component recorded therein reverses its polarity for successive line intervals. Such pattern of recording insures that, during playback or reproduction, cross talk effects can be minimized or eliminated. For example, during reproduction of the recorded signals, the reproduced signals of two successive line intervals may be added together by means of suitable delay means, for example, by a simple comb filter, to cancel out, or at least minimize cross-talk interference signals associated with the desired reproduced signals of the two successive line intervals.
However, in the above-described system for recording and reproducing a color television signal, each of the audio signals thereof, for example, the stereophonic left and right signals, is supplied to a respective fixed head which is continuously in contact with the magnetic tape adjacent a longitudinal edge of the latter so that the stereophonic left and right signals are respectively recorded in audio tracks extending longitudinally along the magnetic tape.
It will be appreciated that, when high density recording of the color video signal in successive slant tracks on the tape is effected as described above, the rotational speed of the rotary magnetic heads is relied upon to provide the desired relatively high speed of each rotary magnetic head in respect to the magnetic tape for ensuring high quality recording of the color video signal in the slant or skewed tracks. However, for achieving the high density recording of the color video signal, the transport speed of the magnetic tape is necessarily quite low, for example, about 1.33 cm/sec. Thus, the relative velocity between the magnetic tape and the fixed heads which record the audio signals in the respective audio tracks is quite low with the result that the quality of the audio recording is deteriorated.
In order to solve the above problem associated with the recording of the audio signals, it has been proposed that the audio signals be frequency-modulated and then mixed with the composite color video signal to provide a mixed or combined signal supplied to the rotary magnetic heads for recording by the latter in the slant tracks. Although the foregoing proposal ensures that the relative speed of the rotary magnetic heads in respect to the magnetic tape will be sufficient to ensure that the recording quality of the audio signals will not be deleteriously affected by an inadequate head-to-tape speed, the reproduced audio signals are still of insufficient quality. More particularly, in the existing proposal for recording frequency-modulated audio signals along with the composite color video signal in the slant tracks on the magnetic tape, the frequency-modulated audio signals recorded in the next adjacent tracks have the same carrier frequency. Therefore, each audio signal reproduced from a particular track contains a zero beat interference due to the audio component of the cross talk from the adjacent tracks even though the level of such cross talk may be reduced by the previously mentioned azimuth loss.
When the audio signals are recorded in the longitudinal tracks on the magnetic tape and also frequency-modulated and mixed with the composite color video signal and recorded in the slant tracks, a reproducing machine must detect the presence of the frequency-modulated audio signals and select them for reproduction. Also, in certain instances, the frequency-modulated audio signals cannot be reproduced from the composite color video signal due to, for example, a drop-out or the like. Since the audio signals are also recorded in the longitudinal track, the reproducing device can reproduce the audio signals therefrom in such an instance and no gap or silence will occur in the reproduced audio signal insofar as the listener or viewer is concerned.
It is important that magnetic tape having the audio signals recorded in the slant tracks be compatible with existing video tape recording and/or reproducing apparatuses which can only reproduce audio signals from the longitudinally disposed tracks. Accordingly, the audio signals must be recorded in both the longitudinal tracks and in the slant tracks so that the magnetic tape can be used with existing video tape recording and/or reproducing apparatuses and video tape recording and/or reproducing apparatuses especially built to reproduce the FM audio signals.
It is sometimes desirable to perform an "audio dubbing" operation with respect to a recorded audio signal, in which an audio signal is recorded later over an existing audio signal. When the audio signals are frequent modulated and mixed with the composite color video signal, it is not possible to perform such a dubbing operation with such mixed signals. Thus, any audio dubbing must be performed with respect to the audio signals recorded in the longitudinal tracks on the magnetic tape.